Physical Principles of Respiratory Care PDF

Physical Principles of Respiratory Care Dr. Jameel Hakeem PhD, RTT Respiratory Department Dr. Jameel Hakeem  Objectives Describe the properties that characterize the three states of matter Descri...

Physical Principles of Respiratory Care Dr. Jameel Hakeem PhD, RTT Respiratory Department Dr. Jameel Hakeem  Objectives Describe the properties that characterize the three states of matter Describe how substances undergo a change of state Describe how water vapor capacity, absolute humidity, and relative humidity are related. Describe how to predict gas behavior under changing conditions, including at extremes of temperature and pressure Dr. Jameel Hakeem  References for this Lecture 3 Dr. Jameel Hakeem  Objectives Describe the properties that characterize the three states of matter Dr. Jameel Hakeem  States of Matter ▪ Three primary states of matter: solids, liquids, gases ▪ Solids ▪ Have high degree of internal order ▪ Fixed volume and shape ▪ Strong mutual attractive force between atoms 5 Dr. Jameel Hakeem  States of Matter (Cont.) ▪ Liquids ▪ Have fixed volume, but adapt to shape of their container ▪ Atoms exhibit less degree of mutual attraction compared with solids ▪ Shape is determined by numerous internal and external forces ▪ Gases ▪ No fixed volume or shape; weak attractive forces ▪ Gas molecules exhibit rapid, random motion with frequent collisions 6 Dr. Jameel Hakeem  Internal Energy of Matter ▪ The atoms that make up all matter are in constant motion at normal temperature ▪ This motion results from internal energy ▪ Two major types of internal energy: ▪ Potential energy ▪ Energy of position (attractive forces between molecules) ▪ Weak in gas state ▪ Makes up most of internal energy in solids and liquids ▪ Kinetic energy ▪ Energy of motion ▪ Makes up most of gases internal energy 7 Dr. Jameel Hakeem  Laws of Thermodynamics The science of studying the properties of matter at various temperatures or the kinetics (speed) of reactions of matter at various temperatures. ▪ Energy cannot be created or destroyed: energy can only be transferred 8 Dr. Jameel Hakeem  Law of thermodynamics Heat transfer ▪ First law of thermodynamics ▪ When two objects of different temperatures coexist, heat will move from hotter to cooler object until both are equal 9 Dr. Jameel Hakeem  Law of thermodynamics ▪ Heat transfer can occur in four ways: ▪ Conduction: Main method of heat transfer in solids ▪ Via direct contact between molecules ▪ Convection: Mixing of fluid molecules at different temperatures ▪ Transfers heat in liquids and gases (e.g., forced air heating in homes-fluid movements carry heat) ▪ Radiation: Occurs without direct contact between two substances ▪ Evaporation and condensation: Form of vaporization, change of state from liquid to gas, or gas to liquid 10 Dr. Jameel Hakeem  11 Dr. Jameel Hakeem  Properties of Liquids ▪ Archimedes’ Principle and Buoyancy ▪ Buoyancy: occurs because pressure below submerged object always exceeds the pressure above ▪ Archimedes’ Principle ▪ Definition: when a body is wholly or partially immersed in a fluid, an upward force acts on it which is equal to the weight of fluid displaced. 12 Dr. Jameel Hakeem  Archimedes Principle ▪ An object submerged in water appeared to weigh less than it did in the air. This effect, called buoyancy ▪ Liquids exert buoyant force ▪ Gases also exert buoyant force, although much less than that provided by liquids ▪ Buoyancy helps keep solid particles suspended in gases. These suspensions are called aerosols. 13 Dr. Jameel Hakeem  Properties of Liquids ▪ Viscosity: force opposing fluid’s flow ▪ Blood has viscosity five times greater than water ▪ Fluid ’ s viscosity is directly proportional to cohesive forces between its molecules ▪ The stronger the cohesive forces, the greater the fluid viscosity ▪ Heart must use more energy when blood viscosity increases, as occurs in polycythemia (increase in red blood cell concentration) 14 Dr. Jameel Hakeem  Properties of Liquids (Cont.) ▪ Cohesion and adhesion ▪ Adhesion: is the attraction between the molecules of two different substances ▪ Cohesion: is the attraction between the molecules or atoms of the same substance ▪ Surface tension: the force exerted by like molecules at the liquid ’ s surface (why bubbles retain spherical shape) 15 Dr. Jameel Hakeem  Surface Tension ▪ Within the lungs, this occurs at the interface between the alveolar membrane and the airway. ▪ Increased surface tension increases cohesion within the alveoli, pulling the alveoli closed 16 Dr. Jameel Hakeem  Properties of Liquids ▪ Pascal’s principle state that liquid pressure depends: ▪ Only on the height (h) and not on the shape of the vessel or the total volume of liquid. ▪ On height and weight density of the liquid. 17 Dr. Jameel Hakeem  Properties of Liquids Capillary action ▪ A phenomenon in which a liquid in a small tube moves upward against gravity A: Adhesion and surface tension contribute to capillary action (capillarity). B : The liquid rises highest in the smallest tube. 18 Dr. Jameel Hakeem  FLUID DYNAMICS ▪ Study of fluids in motion = hydrodynamics ▪ Pressure exerted by liquid in motion depends on nature of flow itself ▪ Progressive decrease in fluid pressure occurs as fluid flows through tube due to resistance (as the velocity increases, the pressure decreases). ▪ Flow resistance is a measure of the opposition to the flow of a fluid through a system or a component 19 Dr. Jameel Hakeem  Fluid Dynamics (Cont.) A, The pressure is the same at all points along the horizontal tube when there is no flow. B, A progressive decrease in pressure occurs as the fluid flows. 20 Dr. Jameel Hakeem  Patterns of Flow ▪ Laminar Flow: fluid flows in parallel layers, with no disruption between the layers ▪ Turbulent Flow is a flow regime characterized by chaotic property changes ▪ Fluid density (d), Viscosity (n), Linear velocity (v), Tube radius(r) ▪ Transitional Flow ▪ It is a mixture of laminar and turbulent flow ▪ When flow is transitional, the total driving pressure equals the sum of the pressures resulting from laminar and turbulent flow 21 Dr. Jameel Hakeem  Bernoulli Principle ▪ As a fluid flows through the constriction, its velocity increases, and its lateral pressure decreases. Lateral pressure of a flowing fluid must vary inversely with its velocity. Vሶ a, flow in tube “a”; va, velocity in tube “a”; vb, velocity in tube “b”; Vሶ b, flow in tube “b”; Pa, lateral wall pressure in tube “a”; Pb, lateral wall pressure after restriction 22 Dr. Jameel Hakeem  Fluid Entrainment ▪ When a flowing fluid encounters a very narrow passage, its velocity can increase greatly. ▪ In some cases, the increase in velocity can be so great as to cause the fluid’s lateral pressure to fall below that exerted by the atmosphere (i.e., to become negative). ▪ If an open tube is placed distal to such a constriction, this negative pressure can pull another fluid into the primary flow stream 23 Dr. Jameel Hakeem  Venturi Mask ▪ The reduced pressure within the restriction may be used to introduce gases (usually air) into a low- pressure region of gas flow 24 Dr. Jameel Hakeem  Objectives Describe how substances undergo a change of state Dr. Jameel Hakeem  Change of State ▪ Liquid-solid phase changes ▪ Melting = changeover from solid to liquid state ▪ Melting point = temperature at which melting occurs ▪ Freezing = opposite of melting ▪ Freezing point = temperature at which substances freeze; same as its melting point ▪ Sublimation = transition from solid to vapor without becoming liquid as an intermediary form ▪ Occurs because vapor pressure is low enough (e.g., dry ice) 26 Dr. Jameel Hakeem  Objectives Describe how water vapor capacity, absolute humidity, and relative humidity are related. Dr. Jameel Hakeem  Temperature ▪ Temperature and kinetic energy are closely related. ▪ Temperature is a measurement of heat. ▪ Heat is the result of molecules colliding with one another. ▪ The temperature of a gas, with most of its internal energy spent keeping molecules in motion, is directly proportional to its kinetic energy. ▪ In contrast, the temperatures of solids and liquids represent only part of their total internal energy. 28 Dr. Jameel Hakeem  Temperature ▪ Fahrenheit (F) and Celsius (C) scales based on the property of water ▪ 0° C is the freezing point of water ▪ −273° C = kinetic molecular activity stops = 0° K ▪ Kelvin scale (° K ) based on molecular motion ▪ Used by SI (International System of Units) units ▪ Zero point = to absolute zero ▪Lowest possible temperature that can be achieved ▪Temperature at which there is no kinetic energy 29 Dr. Jameel Hakeem  Temperature ▪ Conversions: ▪ ° K = ° C + 273 ▪ ° C = 5/9 (° F − 32) ▪ ° F = 9/5 °C + 32 30 Dr. Jameel Hakeem  Liquid-to-vapor phase changes ▪ Boiling (Vaporization): the liquid evaporates when the vapor pressure is greater than atmospheric pressure. ▪ Liquid oxygen boils at −183°C ▪ Evaporation—when liquid changes into gas at a temperature below its boiling point ▪ Water enters the atmosphere via evaporation when at a temperature lower than its boiling point (water vapor) ▪ Molecular water exerts pressure called water vapor pressure ▪ Temperature influences evaporation most ▪ The warmer the air, the more vapor it can hold ▪ Condensation ▪ Opposite of evaporation ▪ Gas becomes a liquid 31 Dr. Jameel Hakeem  Absolute humidity ▪ Also known as water vapor content ▪ Actual amount (or weight) of water vapor in gas ▪ Measured in mg/L ▪ Varies with temperature and pressure ▪ Air expands in low pressure, and vapor is spread in greater volume ▪ Air that is fully saturated with water vapor has absolute humidity of 43.8 mg/L at 37° C, 760 mm Hg, and water vapor pressure of 47 mm Hg 32 Dr. Jameel Hakeem  Relative humidity (RH) ▪ When gas is not fully saturated ▪ Water vapor content can be expressed in relative terms ▪ Ratio of its actual water vapor content to its saturated capacity at a given temperature ▪ %RH = Content (Absolute Humidity)/Saturated Capacity × 100 ▪ Condensation: slight cooling of gas causes its water vapor to turn back into a liquid state ▪ Temperature at which this happens = dew point ▪ 100% RH still exists ▪ High temperatures increase vaporization ▪ The greater the surface area of the gas in contact with air, the greater the rate of liquid evaporation 33 Dr. Jameel Hakeem  Relative humidity (RH) 34 Dr. Jameel Hakeem  Objectives Describe how to predict gas behavior under changing conditions, including at extremes of temperature and pressure Dr. Jameel Hakeem  Properties of Gases ▪ Kinetic activity of gases ▪ Gas molecules travel at high speeds in a random fashion with frequent collisions ▪ Velocity of gas molecules is directly proportional to its temperature ▪ Molar volume and gas density ▪ Ideal molar volume of any gas = 22.4 L at standard temperature and pressure ▪ Density is the ratio of gas’s mass to its volume ▪ Example: 1 gram of Co2 vs 1 gram of Hydrogen 36 Dr. Jameel Hakeem  Properties of Gases (Cont.) ▪ Gaseous diffusion: movement of molecules from areas of high concentration to areas of lower concentration ▪ Graham’slaw light gases diffuse rapidly, whereas heavy gases diffuse more slowly ▪ Gas pressure ▪ All gases exert pressure ▪ Gas pressure in a liquid is known as gas “tension” ▪ Atmospheric pressure is measured with a barometer 37 Dr. Jameel Hakeem  Properties of Gases (Cont.) ▪ Gas tension is often used to refer to the pressure exerted by gases dissolved in liquids. ▪ The pressure or tension of a gas depends mainly on its kinetic activity ▪ Gravity affects gas pressure. ▪ Gravity increases gas density, increasing the rate of molecular collisions and gas tension; this explains why atmospheric pressure decreases with altitude. 38 Dr. Jameel Hakeem  39 Dr. Jameel Hakeem  Gas pressure (Cont.) Dalton’s law The partial pressure of gas in the mixture is proportional to its percentage in the mixture. Partial pressure = pressure exerted by single gas in gas mixture Henry’s law Solubility of gases in liquids at a constant temperature or the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid. High temperatures decrease solubility, and low temperatures increase solubility. Example: Higher temperature will cause higher PaO2 and PaCO2 in ABG. 40 Dr. Jameel Hakeem  Boyle’s law ▪ With constant temperature, the volume and pressure are indirectly proportional ▪ As the pressure is increased, the volume will decrease ▪ Breathe in and breathe out ▪ Boyle’s law is used in pulmonary function labs that perform body plethysmography 41 Dr. Jameel Hakeem  The Charles law ▪ It states that with pressure constant, the volume of a gas is directly proportional to its temperature ▪ A warm gas will take up more volume than a cooler gas at the same pressure. 42 Dr. Jameel Hakeem  The Gay-Lussac’s law (combined gas laws) ▪ At constant volume, pressure and temperature are directly proportional to one another. ▪ As a gas is cooled, the pressure will decrease, and as the gas is heated, the pressure will increase. 43 Dr. Jameel Hakeem  Thank you 44 Dr. Jameel Hakeem